Generators for generating band-limited noise are conventionally implemented using digital technology as analog circuits cannot fulfill the often elevated requirements for low undulation in the noise spectrum, high edge steepness of the noise spectrum and a low signal level outside of the noise spectrum. Such digital noise generators fill the noise spectrum with a (conventionally high) number of equidistant signal lines (individual sinusoidal signals) and generate a severely limited noise spectrum. It is also possible to generate a noise spectrum with gaps using noise generators of this kind. However, the associated noise signals (in the time domain) often have a high crest factor, and in real applications this leads to intermodulation owing to the non-linearities of the amplification stages in the analog signal path, resulting in broadening of the noise spectrum and whereby large numbers of interfering components outside of the desired noise spectrum occur. To solve this problem suitable signal line phase relations with each other are sought. A phase optimization method is described in “Multitone Signals with low Crest Factor; Stephen Boyd, IEEE Transactions on Circuits and Systems, vol. CAS-33, No. 10”, by way of example, which determines the phases of the individual signal lines according to:
      φ    k    =                    π        ⁡                  (                      k            -            1                    )                    2        N  
However, it is not possible to generate a noise spectrum with gaps and a low crest factor using this method.
In certain applications the requirements for minimal interfering components outside of the desired noise spectrum is particularly high, however. By way of example, particularly high requirements in relation to the interfering components outside of the desired frequency spectrum are placed on noise generators which are meant to suppress reception of certain mobile communications frequencies in aircraft. The noise spectra that are to be generated by such generators conventionally have gaps. These requirements cannot be fulfilled by noise generators according to the prior art.
DE 10 2007 038 148 A1 describes a method which by summing the outputs of a plurality of noise-FM signals generates a dither that is both band-limited and also better approximates a uniform probability distribution.
WO 03/039046 A1 discloses a simulator for radio channels which generates noise signals by summing several partial noise signals. The crest factor of a noise signal generated in this manner cannot be sufficiently reduced using this method, however.
U.S. Pat. No. 5,008,845 discloses a method for generating fast sweep signals (chirps) whose spectrum exhibits a flat characteristic. The problem of generating a signal with minimal crest factor is not solved by this method either.